It is well known to provide EAS systems in retail establishments to prevent or deter theft of goods. In a typical system, markers, which are secured to goods, are designed to interact with an electromagnetic or magnetic field placed at a store exit. If the marker is brought into the field or "interrogation" zone, the presence of the marker is detected by the EAS system and an alarm is activated. Some markers of this type are intended to be removed at the checkout counter upon payment for the goods. Other types of markers are deactivated upon checkout by a deactivation device which changes an electromagnetic or magnetic characteristic of the marker so that the marker will no longer be detectable at the interrogation zone.
One type of magnetic EAS system is referred to as a harmonic system because it is based on the principle that a magnetic material passing through an electromagnetic field having a selected frequency disturbs the field and produces harmonic perturbations of the selected frequency. The detection system is tuned to recognize certain harmonic frequencies, and, if present, causes an alarm. The harmonic frequencies generated are a function of the degree of non-linearity of the hysteresis loop of the magnetic material. Such EAS systems have proven to be very effective and are in widespread use.
When using this type of system, it has been customary for employees of a retail establishment to attach the markers to the goods at the establishment. Generally, employees of a store attach markers to goods by means of a pressure sensitive adhesive layer provided on the marker, or, when the marker is intended to be removable, by a mechanical clamping device.
It has been proposed, however, that manufacturers attach or incorporate the markers in their goods before shipment to stores. This practice has been referred to as "source tagging" which means that an EAS marker or "tag" is applied to goods at the "source" or place of manufacture of the goods.
This practice has been adopted to help prevent theft of disc-like devices, such as compact discs ("CDs"). One example of a surveillance device incorporated in a CD is disclosed in German Patent No. 42 42 992 A1 ("Cosnard"). The Cosnard patent discloses EAS magnetic strips or security foil embedded in the plastic portion surrounding the aperture of the CD. Another example is disclosed in U.S. Pat. No. 5,347,508 ("Montbriand et al.") which discloses an annular EAS magnetic marker concentrically oriented and positioned in an annular groove located around the aperture of the CD.
This placement of EAS strips, foil or markers in a CD helps to alleviate attaching markers to CDs at the retail establishment, but may result, however, in hindering the functioning of the CD, the strip or marker or the CD drive or player. In addition, if the strip or marker is not precisely embedded in the CD, a misplacement can cause interference with the functioning of the CD drive or player. Further, the aluminum coating of the CD can cause interference with the output signal level of the EAS strip or marker thus reducing its signal output which may prevent detection of the strip or marker by surveillance.
It is, therefore, an object of the present invention to provide a disc-like device having a magnetic material layer which provides detection by an EAS detection system.
It is an additional object of the present invention to provide a disc-like device having a magnetic material layer which is combineable or integrated with the disc-like device.
It is a further object of the present invention to provide a disc-like device having a magnetic material layer which is not noticeable or removable from the device.
It is another object of the present invention to provide a disc-like device having a magnetic material layer which can be incorporated in the device at the place of manufacture.